It relates more particularly to electromagnetic equipment usable to stir the metal which remains liquid inside the product as it moves along the casting line. As it moves, the cast product cools and solidifies little by little from its surface, and it is conventional practice to stir the metal which is still liquid, since moving said metal improves the final metallurgical quality of the cast product. This motion is generated by electro-magnetic induction and is referred to as "electromagnetic stirring". Industrially, such stirring is performed at one or more levels along a continuous casting line: level with the ingot mold (referred to as level M by the person skilled in the art); beneath the mold in the secondary cooling zone (level S); and at the bottom of the solidification well (level F).
Stirring can be obtained by means of a moving magnetic field which may be rotating or sliding, and which penetrates into the cast product.
These magnetic fields are produced by polyphase static inductors placed as close as possible to the cast product. Rotating fields are produced by "rotary" inductors and sliding fields are produced by "linear" inductors.
When it is desired to stir in a plane which is perpendicular to the casting axis, rotary stirring is suitable for products which are round, square, or only slightly oblong, i.e. products which are nearly square in section, such as billets and blooms. In such applications, the rotary inductor provides the best achievable penetration of the magnetic induction into the core of the cast product and thus acts effectively throughout the bulk of the liquid to be stirred.
In contrast, linear stirring is suitable for flat products, such as slabs.
Prior rotary inductors have always been constructed in such a manner as to create magnetic induction which passes through the cast product perpendicularly to the casting axis, with the induction being caused to rotate about said axis by feeding the inductor with polyphase electricity (generally two-phase for a square inductor and three-phase for a round inductor). In order to ensure that the magnetic field rotates uniformly, the inductor completely surrounds the cast product. More precisely, a rotating field inductor which does not completely surround the cast product has neither been manufactured nor proposed in public, and it has seemed economically impossible to use a rotating field when the configuration of the continuous casting machine at the level at which the stirring is to be performed is not suitable for allowing the inductor to completely surround the cast product.
Under such circumstances, a linear inductor has been used disposed over the most accessible face of the casting line or over its only accessible face. In other words the lower efficiency of such an inductor has been accepted in cases where rotary stirring would be the most effective.
In order to benefit from the effectiveness of rotary stirring in spite of the problem posed by the lack of available space around the casting line, a first solution could be to make use of a plurality of partial inductors which are mechanically separate but which are electrically and magnetically coupled, and to dispose the partial inductors symmetrically around the cast product so as to cause them to produce a rotating field like a conventional single rotary inductor. However, this solution does not always overcome all of the difficulties encountered for locating a rotating field inductor on a pre-existing continuous casting line.
This may happen when the path followed by the metal is vertical on leaving the mold and then curves progressively to the horizontal. This curvature of the casting line forms a concave side and a convex side. If rotary stirring is then to be performed immediately below the mold at a location where the skin of solidified metal on the surface of the cast product is still thin and where it is consequently essential to guide the cast product over substantially all of its perimeter and along a certain distance by supporting rolls which are very close to one another, and if, in addition, the inductor cannot be disposed within the rolls because of the relatively high stirring power which is to be applied, it is then necessary to dispose the inductor around the rolls. But this can be done easily only by applying the inductor or the two half inductors from the concave side of the line because the convex side is occupied by the beams which constitute a support structure for supporting the casting line as a whole. This way of inserting the inductor generally requires the first guide segment (i.e. the structure which includes and supports the rolls) to be removed in order to put the inductor or one of the two half inductors in place or to remove it, and this gives rise to considerable constrains in maintenance and assembly operations.
Other cases can also occur in which it is difficult or even impossible to put two half inductors or a single rotary inductor of conventional design into place because of the configuration of the casting line, assuming that prior art types of rotary field inductor are the only kind available.
An object of the present invention is to make it possible and easy to install, operate, maintain, and replace an inductor device in most of those cases where the configuration of the continuous casting line under consideration would appear to present difficulties at the intended stirring level.